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In this paper, we present a set of photometric observations in 15 colors of stars in the Landolt SA95 field with the BATC system. The wavelengths covered by the system range from 300 nm to 1000 nm. Visual magnitudes of the stars studied in the field are from the 10th to 20th mag. The observational methodology and the data reduction procedures are described. The relationships between the BATC intermediate-band system and the Landolt UBVRIbroad band system are obtained. A catalogue of the photometry has been produced which contains the SEDs of 3613 stars.

Absolute proper motions for ?7.7 million objects were derived based on data from the South Galactic Cap u-band Sky Survey (SCUSS) and astrometric data derived from uncompressed Digitized Sky Surveys that the Space Telescope Science Institute (STScI) created from the Palomar and UK Schmidt survey plates. We put a great deal of effort into correcting the position-, magnitude-, and color-dependent systematic errors in the derived absolute proper motions. The spectroscopically confirmed quasars were used to test the internal systematic and random error of the proper motions. The systematic errors of the overall proper motions in the SCUSS catalog are estimated as -0.08 and -0.06 mas/yr for ??cos ? and ??, respectively. The random errors of the proper motions in the SCUSS catalog are estimated independently as 4.2 and 4.4 mas/yr for ??cos ? and ??. There are no obvious position-, magnitude-, and color-dependent systematic errors of the SCUSS proper motions. The random error of the proper motions goes up with the magnitude from about 3 mas/yr at u= 18.0 mag to about 7 mas/yr at u= 22.0 mag. The proper motions of stars in SCUSS catalog are compared with those in the SDSS catalog, and they are highly consistent.

The South Galactic Cap u-band Sky Survey (SCUSS) provides a deep u-band imaging of about 5000 deg2in south Galactic cap. It is about 1.5 mag deeper than the SDSS u-band. In this article, we evaluate the capability of quasar selection using both SCUSS and SDSS data, based on considerations of the deep SCUSS u-band imaging and two-epoch u-band variability. We find that the combination of the SCUSS u-band and the SDSS griz-band allows us to select more faint quasars and more quasars at redshift around 2.2 than the selection that uses only the SDSS ugrizdata. Quasars have significant u-band variabilities. The fraction of quasars with large two-epoch variability is much higher than that of stars. The selection by variability can select both low-redshift quasars with ultraviolet excess and mid-redshift (2 < z< 3.5) quasars where quasar selection by optical colors is inefficient. The above two selections are complementary and make full use of the SCUSS u-band advantages.

An optical photometric observation in 15 bands was carried out for the nearby galaxy cluster Abell 1775 (A 1775) by the Beijing-Arizona-Taiwan-Connecticut (BATC) multi-color system. Over 5000 sources’ spectral energy distributions (SEDs) were obtained. Since this cluster has also been observed by the Sloan Digital Sky Survey (SDSS), the BATC SEDs were combined with the SDSS five-band photometric data. Using the combined SEDs, 146 faint galaxies were selected as new member galaxies by the photometric redshift technique. Based on the positions, redshifts, and 20-band SEDs of member galaxies, dynamical substructures and luminosity functions (LFs) of A 1775 were investigated. The previous reported bimodal structure of A 1775 has been confirmed: a poor subcluster with lower redshift, A 1775 A, is located $\sim$14$\prime$southeast to the main concentration, A 1775 B. After taking into account the new supplemented member galaxies, a new subcluster, A 1775 C, was found along the aligned direction of A 1775 A and A 1775 B. The different LF faint ends of the two subclusters indicate that A 1775 B is a more dynamically evolved system, while A 1775 A is still dynamically young. By using the STARLIGHT spectral synthesis code, the star-formation histories of the member galaxies were studied. The dependence of the mean stellar ages upon the Hubble type was confirmed, and the environmental effect on star-formation activities for galaxies in A 1775 B has been explored.

M31 globular cluster B379 is the first extragalactic cluster whose age was determined by main-sequence photometry. In the main-sequence photometric method, the age of a cluster is obtained by fitting its color-magnitude diagram (CMD) with stellar evolutionary models. However, different stellar evolutionary models use different parameters of stellar evolution, such as range of stellar masses, different opacities and equations of state, and different recipes, and so on. So, it is interesting to check whether different stellar evolutionary models can give consistent results for the same cluster. Brown et al. constrained the age of B379 by comparing its CMD with isochrones of the 2006 VandenBerg models. Using SSP models of Bruzual & Charlot and its multiphotometry, ZMa et al. independently determined the age of B379, which is in good agreement with the determination of Brown et al. The models of Bruzual & Charlot are calculated based on the Padova evolutionary tracks. It is necessary to check whether the age of B379 as determined based on the Padova evolutionary tracks is in agreement with the determination of Brown et al.. In this article, we redetermine the age of B379 using isochrones of the Padova stellar evolutionary models. In addition, the metal abundance, the distance modulus, and the reddening value for B379 are reported. The results obtained are consistent with the previous determinations, which include the age obtained by Brown et al. This article thus confirms the consistency of the age scale of B379 between the Padova isochrones and the 2006 VandenBerg isochrones; i.e., the comparison between the results of Brown et al. and Ma et al. is meaningful. The results reported in this article of values found for B379 are: metallicity [M/H] = log(Z/Z?) = -0.325, age ? = 11.0 ± 1.5 Gyr, reddening E(B- V) = 0.08, and distance modulus (m- M)0= 24.44 ± 0.10.

We present the correlations between the spectroscopic metallicities and 93 different intrinsic colors of M31 globular clusters, including 78 Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey colors and 15 SDSS and near-infrared ugrizK colors. The BATC colors were derived from the archival images of 13 filters (from cto p) taken by the Beijing-Arizona-Taiwan-Connecticut Multicolor Sky Survey with a 60/90 cm f/3 Schmidt telescope. The spectroscopic metallicities adopted in our work were from literature. We fitted the correlations of 78 different BATC colors and the metallicities for 123 old confirmed globular clusters, and the result implies that correlation coefficients (r) of 23 colors r> 0.7. For the colors (f- k)0, (f- o)0, and (h- k)0, the correlation coefficients are r> 0.8. Meanwhile, we also note that the correlation coefficients approach zero for (g- h)0, (k- m)0, (k- n)0, and (m- n)0, which are likely to be independent of metallicity. Similarity, we fitted the correlations of metallicity and ugrizK colors for 127 old confirmed GCs. The result indicates that all these colors are metal-sensitive (r> 0.7), and (u- K)0is the most metal-sensitive color. Our work provides a simple way to estimate the metallicity from colors.

In 2008 January the twenty-fourth Chinese expedition team successfully deployed the Chinese Small Telescope ARray (CSTAR) to Dome A, the highest point on the Antarctic plateau. CSTAR consists of four 14.5 cm optical telescopes, each with a different filter (g, r, i, and open) and has a 4.5° × 4.5° field of view (FOV). It operates robotically as part of the Plateau Observatory, PLATO, with each telescope taking an image every ?30 s throughout the year whenever it is dark. During 2008, CSTAR 1 performed almost flawlessly, acquiring more than 0.3 million i-band images for a total integration time of 1728 hr during 158 days of observations. For each image taken under good sky conditions, more than 10,000 sources down to ?16thmagnitude could be detected. We performed aperture photometry on all the sources in the field to create the catalog described herein. Since CSTAR has a fixed pointing centered on the south celestial pole (decl. = -90°), all the sources within the FOV of CSTAR were monitored continuously for several months. The photometric catalog can be used for studying any variability in these sources, and for the discovery of transient sources such as supernovae, gamma-ray bursts, and minor planets.

This paper is the third in a series of papers on M81 globular clusters. In this paper, we present spatial and metal abundance properties of 95 M81 globular clusters, which comprise nearly half the entire M81 globular cluster system. These globular clusters are divided into two M81 metallicity groups by a KMM test. Our results show that the metal-rich clusters did not demonstrate a centrally concentrated spatial distribution the way the clusters in M31 do, and metal-poor clusters tend to be less spatially concentrated. In other words, the distribution of the metal-rich clusters in M81 is not very similar to that of M31. The quick histogram shows that most of the metal-rich clusters are distributed at projected radii of 4-8 kpc. Note also that the metal-rich clusters are distributed within the inner 20 kpc, and the metal-poor ones, out to radii of ?40 kpc. Like our Galaxy and M31, the metallicity distribution of globular clusters in M81 along a galactocentric radius suggests that some dissipation occurred during the formation of the globular cluster system; i.e., smooth, pressure-supported collapse models of galaxies are unlikely to produce the type of radial distribution of metallicity presented in this paper. There is no evident correlation between globular cluster luminosity and metallicity in M81 globular clusters. The overwhelming conclusion of this paper seems to be that a more complete and thorough cluster search is needed in M81.

We have constrained the age of the globular cluster S312 in the Andromeda galaxy (M31) by comparing its multicolor photometry with theoretical stellar population synthesis models. This is both a check on the age of this globular cluster and a check on our methodology. Main-sequence photometry has been the most direct method for determining the age of a star cluster. S312 was observed as part of the Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey from 1995 February to 2003 December. The photometry of BATC images for S312 was taken with nine intermediate-band filters covering 5000-10000 A. Combined with photometry in the near-ultraviolet (NUV) of GALEX, broadband UBVR, and infrared JHKs of 2MASS, we obtained the accurate spectral energy distributions (SEDs) of S312 from 2267-20000 A. A quantitative comparison to simple stellar population models yields an age of 9.5img1.gif Gyr, which is in very good agreement with the previous determination by main-sequence photometry. S312 has a mass of 9.8 +- 1.85 x 105 M and is a medium-mass globular cluster in M31. By analyzing the errors of ages determined based on the SED-fitting method of this paper, secure age constraints are derived with errors of <3 Gyr for ages younger than 9 Gyr. In fact, the theoretical SEDs are not sensitive to the variation of age for ages > ~10 Gyr. Therefore, our method does not accurately distinguish globular clusters (GCs) as old as the majority of the Galactic GCs. We emphasize that our results show that even with multiband photometry spanning from NUV to Ks, our age constraints from SED fitting are distressingly uncertain, which has implications for age derivations in extragalactic globular cluster systems.

Using the galaxy sample observed by the Beijing-Arizona-Taiwan-Connecticut (BATC) large-field multicolor sky survey and the galaxy data of the Sloan Digital Sky Survey (SDSS) in overlapping fields, we study the dependence of the rest-frame r-band galaxy luminosity function on redshift and on the large-scale environment. The large-scale environment is defined by isodensity contours with density contrast dr/r. The data set is a composite sample of 69,671 galaxies with redshifts 0.03 < z < 0.5 and r < 21.5 mag. The redshift data are composed of three parts: (1) spectroscopic redshifts in SDSS for local and the most luminous galaxies, (2) 20-color photometric redshifts derived from BATC and SDSS, and (3) five-color photometric redshifts in SDSS. We find that the faint-end slope a steepens slightly from -1.21 at z ~ 0.06 to -1.35 at z ~ 0.4, which is the natural consequence of the hierarchical formation of galaxies. The luminosity function also differs with different environments. The value of a changes from -1.21 in underdense regions to -1.37 in overdense regions, and the corresponding M* brightens from -22.26 to -22.64. This suggests that the fraction of faint galaxies is larger in high-density regions than in low-density regions.

In this paper, we give the spectral energy distributions (SEDs) of 42 M81 globular clusters in 13 intermediate-band filters from 4000 to 10000 Å using the CCD images of M81, observed as part of the Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey. The BATC multicolor filter system is specifically designed to exclude most of the bright and variable night-sky emission lines, including the OH forest. Hence, it can present accurate SEDs of the observed objects. These SEDs are low-resolution spectra and can reflect the stellar populations of the globular clusters. This paper confirms the conclusions of Schroder et al., that M81 contains clusters as young as a few Gyr, which were also observed in both M31 and M33.

This paper includes two parts. The first presents the spectral energy distributions (SEDs) of 49 globular cluster (GC) X-ray sources in 13 BATC (Beijing-Arizona-Taiwan-Connecticut) intermediate-band filters from 3800 to 10000 Å, and identifies 8 previously unidentified X-ray sources in M31. Using X-ray data from Einsteinobservations from 1979 to 1980, ROSATHigh Resolution Imager observations in 1990, ChandraHigh Resolution Channel and ACIS-I observations from 1999 to 2001, and the BATC optical survey from 1995 to 1999, we find 49 GC X-ray sources and 8 new X-ray sources in the BATC M31 field. By analyzing SEDs and FWHMs, we determine that 4 of the 8 X-ray sources may be GC candidates. The second part presents some statistical relationships between 62 GC X-ray sources, of which 58 are already known and 4 are identified in this paper. The distribution of M31's GC X-ray sources' Vmagnitudes is bimodal, with peaks at mv= 15.65 and 17.89, which is different from the distribution of GC candidates. The distribution of B - V color shows that the GC X-ray sources seem to be associated preferentially with the redder GCs, in agreement with previous results. Kolmogorov-Smirnov test shows that the maximum value of the absolute difference of B - V distributions of GC X-ray sources and GCs is Dmax= 0.181, and the probability P = 0.068, which means we can reject the hypothesis that the two distributions are the same at the 90.0% confidence level. Finally, we study the correlation between X-ray luminosity (0.3-10 keV) and optical luminosity (in the Vband) of the GC X-ray sources in M31, and find that there exits a weak relationship with the linear correlation coefficient r = 0.36 at a confidence level of 98.0%.

In this paper we present catalogs of photometric and spectroscopic data for globular clusters (GCs) in M81. The catalogs include B- and V-band photometric and reddening data of 95 GCs, in addition to spectroscopic metallicities of 40 GCs. Using these data, we make some statistical correlations. The results show that the distributions of intrinsic Band Vcolors and metallicities are bimodal, with metallicity peaks at [Fe/H] ? - 1.45 and ?0.53, respectively, as has been demonstrated for our Milky Way and M31. The relation between spectroscopic metallicity and intrinsic Band Vcolor also exists as it does for the Milky Way and M31.

This paper presents a multicolor study of the nearby cluster of galaxies A168 (z = 0.045) with 13 intermediate-band filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) filter system. After a cross-identification between the photometric data obtained from the BATC and the Sloan Digital Sky Survey (SDSS), a catalog containing 1553 galaxies down to r' < 20.0 mag is achieved, which includes 121 spectroscopically confirmed member galaxies. The technique of photometric redshift has been applied to all these galaxies with combined 18 band (13 from BATC and five from SDSS) spectral energy distributions (SEDs), in order to perform a faint membership selection in A168. As a result, 255 galaxies are newly selected as the member candidates. On the basis of the enlarged sample of cluster galaxies, the spatial distribution and dynamics of A168 are investigated. In light of the spatial distribution of the member galaxies and the 0.2-3.5 keV X-ray image by the Einstein X-Ray Observatory, it seems that A168 consists of two merging subclusters with a relative radial velocity of 264 +- 142 km s-1. With the help of ROSTAT software, a detailed investigation of the dynamics shows the intrinsic difference in the velocity distributions for these two subclusters. Under a linear two-body model, they are found to be a gravitationally bound system with 92% probability. The slight deviation of the local velocity distribution from the overall distribution in the central region may suggest a picture of head-on collision in the projection plane. By using a double Schechter function, the close examination of the luminosity functions reveals the different galaxy content of these two subclusters, which implies that the merging process is possibly at the early stage.

We present a complete set of 16 color photometric observations in the Beijing-Arizona-Taipei-Connecticut (BATC) filter system for a cluster of galaxy Abell 566 at redshift $z \simeq 0.1$. From $2 \,\mathrm{k} \times 2 \,\mathrm{k}$CCD images, over 10000 objects have been detected in field of $58' \times 58'$down to $V \sim 20 \,\mathrm{mag}$with a good completeness level. By aperture photometric measurements, we obtained spectral energy distributions (SEDs) that cover the wavelengths from 300 nm to 1000 nm of all of the detected objects, including 561 cluster member candidates selected by the method of photometric redshift. The special location of these galaxies in color-color diagrams show a possibility for our method involving member galaxy selection. From the selected member galaxies, we find that the number density of early-type galaxies is much higher in the central region of the cluster than late-type galaxies.

This paper summarizes the measurements of astronomical observing conditions with a fixed pointing to the North Pole over 6 years at the Xinglong Station, where the BATC Multicolor Sky Survey has been conducted since 1995. Three major effects that influence the sky quality the most have been studied: the atmospheric transparency, the sky brightness, and the seeing. No obvious annual variation of the transparency was detected, but seasonal changes on a regular basis have been observed. The transparency is better and more stable in the winter than in the summer, which points to the fact that winter is the season for precise photometric work in Xinglong. The relations of sky brightness versus lunar phase and versus lunar altitude are derived and discussed. We find, on average, that the value of sky brightness in moonlight-corrected Vmagnitude of the North Pole field is about 21.0 mag arcsec?2. The sky is darker in the fall and winter than in the spring and summer, and the transparency is better. It is conjectured that there are fewer particles in the air in the winter, thus both absorption and scattering are minimal. The seeing in the winter is worse than in the summer. This is probably due to the gusty wind from the northwest in the winter. The results of the North Pole monitoring presented in this paper show that the Xinglong Station is an astronomically good observing site. The North Pole observations will continue as a part of the BATC sky survey.

In this paper, we present the methodology of photometric redshift determination with the BATC 15 color system by using the hyperzprogram. Both simulated galaxies and real galaxies with known redshifts were used to estimate the accuracy of redshifts inferred from multicolor photometry. From the test with simulated galaxies, the uncertainty in the inferred redshifts is about 0.02-0.03 for a given range of photometric uncertainty of 0.05-0.10 mag. The results with the 27 real galaxies are in good agreement with the simulated ones. The advantage of using the BATC intermediate-band system to derive redshift is clear after comparison with the UBVRIbroadband system. The accuracy in redshift determination with the BATC system is mainly affected by the selection of filters and the photometric uncertainties in the observation. When we take the limiting magnitudes of the 15 filters into account, we find that redshift can be determined with good accuracy for galaxies with redshifts less than 0.5, using only filters with central wavelengths shorter than 6000 Å.

Owing to their spectral properties, Herbig-Haro (HH) objects can be discovered using photometric methods through a combination of filters, sampling the characteristic spectral lines and the nearby continuum. The data are commonly processed through direct visual inspection of the images. To make data reduction more efficient and the results more uniform and complete, an automated searching scheme for HH objects is developed to manipulate the images using IRAF. This approach helps to extract images with only intrinsic HH emissions. By using this scheme, the pointlike stellar sources and extended nebulous sources with continuum emission can be eliminated from the original images. The objects with only characteristic HH emission become prominent and can be easily picked up. In this paper our scheme is illustrated by a sample field and has been applied to our surveys for HH objects.

We describe in detail the extinction correction procedures used for the Beijing-Arizona-Taiwan-Connecticut Sky Survey (BATC Survey). The survey covers the spectral range 3200-9900 ? by utilizing a set of 15 intermediate-band filters. These filters are specifically designed to exclude most of the bright and variable night-sky emission lines. We also present extinction coefficients for the filter passbands for typical photometric nights at the Xinglong Observing Station, Beijing Astronomical Observatory (where the observations of the survey are being carried out). Time-dependent, low-amplitude (?1%), nightly extinction variation has been observed. Such variation is demonstrably independent of filter bandpass and air mass, with amplitudes ranging from ?0.01 to ?0.03 mag. The variation is plausibly caused by slowly varying (at ?1%) atmospheric extinction, possibly related to changes in air pressure/temperature/humidity that occur during the night. An iterative fitting scheme has been developed to take this time-varying component into account. We conclude that the survey can achieve its stated observational goal, namely, an absolute photometric calibration that is tied to the AB?system to an accuracy of 1% in all filters.

The purpose of this paper is to present a method to self-calibrate the spectral energy distribution (SED) of objects in a survey based on the fitting of a SED library to observed multicolor photometry. We adopt, for illustrative purposes, the Vilnius and Gunn & Stryker SED libraries. The self-calibration technique can improve the quality of observations which are not taken under perfectly photometric conditions. The more passbands used for the photometry, the better the results. This technique has been applied to the BATC 15 passband CCD survey.

The Beijing-Arizona Sky Survey (BASS) is a wide-field two-band photometric survey of the northern Galactic Cap using the 90Prime imager on the 2.3 m Bok telescope at Kitt Peak. It is a four-year collaboration between the National Astronomical Observatory of China and Steward Observatory, the University of Arizona, serving as one of the three imaging surveys to provide photometric input catalogs for target selection of the Dark Energy Spectroscopic Instrument (DESI) project. BASS will take up to 240 dark/gray nights to cover an area of about 5400 deg2in the gand rbands. The 5?limiting AB magnitudes for point sources in the two bands, corrected for the Galactic extinction, are 24.0 and 23.4 mag, respectively. BASS, together with other DESI imaging surveys, will provide unique science opportunities that cover a wide range of topics in both Galactic and extragalactic astronomy.